Direct gas-fired heating systems provide heated air to buildings by drawing fresh air in from outside the building and heating it to make up for the loss of heated inside air through open doors, exhaust fans, etc. A recirculating direct fired heating system mixes the heated outside air with recirculated inside air before delivering the mixture to the building. The heating system is configured to maintain a selected air pressure and temperature inside the building. For the direct fired heating system to function properly, the air stream over the direct fired burner must be maintained at a constant mass flow rate, which requires that the pressure differential across the burner be maintained at a relatively constant level. If the pressure drop across the burner is too high or too low, the flame from the burner might be too long and risk burning system components, or the air pressure will extinguish the burner flame. In conventional recirculating systems, dampers control the relative amounts of air flow between the recirculated or return air and the outside or make-up air. The systems are set to supply a certain volume of air to the building, and the dampers are positioned so that the return air and the outside air combine to supply the set volume. Conventionally, the dampers for the return air and the outside air are linked either mechanically or electronically so an adjustment to one causes an equal and opposite adjustment in the other. However, this control system does not measure the pressure drop across the burner or maintain a precise targeted pressure difference for optimizing operation of the burner, nor does it allow for changes to the volume of air supplied to the building. One pressure control solution suggested by the prior art is to have a passive damper for regulating the pressure drop across the burner. However, this system cannot keep up with the pressure changes across the burner, and thus the pressure differential is not maintained with sufficient precision. This system also cannot maintain the burner pressure differential when the total air volume changes. There is a need for a direct fired burner heating system that more precisely maintains an optimal flow rate over the burner.